Toxicokinetics of pentachlorophenol (PCP) was studied in male and female F344 rats using iv (5 mg/Kg) and oral gavage (9.5, 38, and 75 mg/Kg) routes. After a bolus iv dose of 5 mg/Kg, PCP plasma concentration data was best fit with a two compartment model in male rats and a one compartment model in female rats. The calculated bioavailability of PCP after oral gavage doses ranged from 47 to 75% which appeared to be related to incomplete GI tract absorption. (Both sexes had a similar rate of GI tract absorption of PCP but the area under concentration versus time curves (AUC) values obtained from both the iv and gavage routes were significantly different with males having higher AUC values.) The theoretical PCP plasma concentrations in a proposed chronic dosed feed study were simulated using a computer model. Results of the simulation suggest that if no significant palatability problems exist, PCP concentrations in rat plasma will fluctuate daily and a quasi-steady state will be achieved after ad libitum exposure to dosed feed for approximately 4 days.